1. Technical Field of the Invention
The invention relates to the field of hot isostatic presses arranged for rapid cooling of articles by causing a cooled pressure medium to circulate through the furnace chamber.
2. Discussion of the Related Art
Hot isostatic presses are known in a variety of designs and utilized, for example, for manufacturing solid bodies starting from a powdered material, or for condensing castings. The press is able to operate within a wide temperature and pressure interval, usually between 500.degree. and 2200.degree. C. and between 500 and 2000 bar. As pressure medium an inert gas, such as argon, is usually used, but also liquid pressure mediums can be used.
The hot isostatic press substantially consists of a pressure chamber in which a furnace is arranged which is usually intended to be heated by means of electric heating elements and which is surrounded by a heat-insulating mantle and a bottom insulation plate. Between the heat-insulating mantle and the pressure vessel wall, which is usually provided with some form of cooling means, a space containing pressure medium is provided which is colder than the furnace chamber.
For many applications it is of interest to be able to rapidly cool the furnace chamber in order for the articles contained therein to attain the proper material properties, and also to make possible a more rapid withdrawal of the articles and thus reduce the cycle time.
To bring about a rapid cooling of the furnace chamber in a hot isostatic press, it is known to provide communication between the furnace chamber and the colder space in the press and allow cold gas from the colder part to circulate through the furnace chamber. It is also possible to effect additional cooling of the gas by allowing it to pass through a heat exchanger or some form of heat-absorbing body. Cooling can also be achieved by providing the press with a device for injecting cold gas from a source outside the press into the furnace chamber. Such a press is known from EP 85200706-1, in which the cooling is effected by allowing an injector, which is connected to a high pressure pipe for cold gas and is mounted inside a housing which communicates through a valve with the space between the chamber wall and the insulating mantle, to inject a mixture of cold gas into the furnace chamber. The insulating mantle around the furnace chamber is provided with openings so as to promote gas circulation.
The disadvantage of the present devices for effecting a rapid cooling of an HIP furnace is that a non-uniform cooling of the material is obtained when gas which is considerably colder than the gas in the furnace chamber flows through the articles. This may lead to an uneven quality of the articles. Also, stresses may arise in the articles which lead to the formation of cracks and result in the articles having to be rejected.